DFT studies on electronic spectra and nonlinear optical properties of symmetric squaraine derivatives linked with borazine

The geometrical structures of symmetric 2,4-squaraine compounds have been optimized by using DFT B3LYP/6-31G(d). On the basis of them, electronic absorption spectra of the compounds were investigated with TD-DFT and second-order hyperpolarizability gamma were calculated by means of finite field (FF) method by introducing an external electronic filed. It is shown from the calculation that the borazine is a donor, different from benzene. Charge population, FMO and NLO properties change distinctly with change of the the atom linked to squaraine. To increase the gamma value of a donor group, the atom linked to other group must be N atom. The best value of gamma in the symmetric squaraine derivatives linked with borazine can reach 2.380 8 X 10(-24) C (.) m.